ENH : first pass at MD_dict to handle nested mete-data

 - can get/set by dotted paths
 - can read/write to hdf groups in compliance with DataExchange
ENH : add json_entry to ArgSpec classes

Dumps the data to a dictionary for use with json
ENH : scaled back tool class

Stripped out json generation code
ENH : first pass at handle registry

decorator which sub-classes the decorated class from each of the
interfaces given.